Gram-positive microorganisms, such as members of the genus Bacillus, have been used for large-scale industrial fermentation due, in part, to their ability to secrete their fermentation products into their culture media. Secreted proteins are exported across a cell membrane and a cell wall, and then are subsequently released into the external media. Secretion of polypeptides into periplasmic space or into their culture media is subject to a variety of parameters, which need to be carefully considered in industrial fermentations.
Indeed, secretion of heterologous polypeptides is a widely used technique in industry. Typically, cells are transformed with a nucleic acid encoding a heterologous polypeptide of interest to be expressed and thereby produce large quantities of desired polypeptides. This technique can be used to produce a vast amount of polypeptide over what would be produced naturally. These expressed polypeptides have a number of industrial applications, including therapeutic and agricultural uses, as well as use in foods, cosmetics, cleaning compositions, animal feed, etc. Thus, increasing expression of polypeptides is of great interest in many fields.